1. Field of the Invention
The present invention relates generally to particulate sampling systems, and more specifically to devices, methods and systems for isokinetic sampling of particulate matter, in-situ, from a high-temperature and/or high-pressure gas stream.
2. Description of Related Art
Various industrial processes generate gas streams containing particulate matter. For example, coal-based power generation technologies produce particulate-loaded streams of process gas. The gas streams are often filtered to remove entrained particulate matter prior to release to the atmosphere to reduce emissions, and/or prior to introduction to process equipment that may be damaged by the particulate matter. For example, particulate control devices (PCDs), such as ceramic barrier filters or granular bed filters can be utilized to remove particulate matter from process gasses produced by coal gasification and combustion prior to their use in a turbine or fuel cell to generate electricity in a power generation plant. Gas turbines utilized in power generation typically require particulate loading in the gas supply stream of less than 20 ppmw (parts per million by weight) or less than 24 mg/m3, with less than one percent of the particulate matter being larger than 10 microns (xcexcm). See McClung, et al., xe2x80x9cDesign and Operating Considerations for an Advanced PFBC Plant at Wilsonvillexe2x80x9d, in Proceedings of the 13th International Conference on Fluidized-Bed Combustion, Vol. 1, pp. 107-115, Published by American Society of Mechanical Engineers, 1995. Increasingly stringent environmental protection regulations typically limit particulate emissions to the environment to 30 ppmw or less, and advanced emission control systems may enable particulate removal to as low as 0.2 ppmw or less.
The characteristics of a gas stream containing particulate matter often must be determined by sampling the gas stream. Sampling may be required to determine the overall quantity of particulate matter in a given volume of gas, to determine the portion of the particulate matter that falls within one or more particle size ranges, and/or to determine various characteristics of the particulate matter or the overall gas stream (such as, for example, chemical content, pH, temperature, pressure, flowrate, etc.). A variety of sampling devices have been developed for these purposes. For example, extractive sampling techniques remove a portion of the particulate-laden gas from the gas stream for processing and/or analysis in an external sampler device. Extractive sampling suffers a number of disadvantages. For example, the particulate properties may be altered during extraction. Various components of the gas stream, such as, for example, alkali or tar vapors in the gas stream, may condense during extraction. To minimize the adverse effects of sample gas cooling, extractive sampling lines must be heat traced, and expensive, high-temperature isolation valves must be used. Unfortunately, these complicated and expensive heat tracing systems are only partially successful in minimizing condensation of gas stream components, and add considerably to the expense of the sampler. In addition, collisions of the particles with one another and with the walls of the sampling lines during extraction alter the particulate content and sizing. See Anand, et al., xe2x80x9cOptimization of Aerosol Penetration Through Transport Lines,xe2x80x9d Aerosol Science and Technology, Vol. 16, pp. 105-112 (1992). Thus, in-situ, isokinetic sampling of the gas stream has been found to be desirable. With an in-situ sampling system, it is not necessary to heat trace the external portion of the system, and it is possible to use less-expensive, low-temperature isolation valves. By allowing the use of less-expensive valves, the in-situ sampling system can be a more cost-effective means of sampling and provides more representative samples when compared to an extractive sampling system.
Enabling in-situ, isokinetic sampling, however, presents a number of challenges. The size of sampling devices for in-situ sampling is often severely constrained by the associated process equipment. For example, in situ sampling of a gas stream flowing within a twelve-inch (12xe2x80x3) process pipe typically requires that the sampler size be considerably less than twelve inches, and not present an unacceptable flow restriction within the pipe. Additional constraints on the size and configuration of a sampling device may result from the sampling technique. For example, a sampler may need to be specially configured for sampling at or near the wall of a process pipe, or at the midpoint of the flow. Access limitations and safety concerns also may dictate the need for remote control of the sampling equipment, and the need for seals, purge systems, and other substantial means for isolating the gas stream from the external environment during sampling.
Further challenges to the successful development of in-situ, isokinetic sampling are presented by the characteristics of the particulate-laden gas stream being sampled. For example, recent and ongoing developments in advanced technologies for power generation, such as coal-based advanced pressurized fluidized-bed combustion (APFBC) and integrated gasification combined cycle (IGCC) processes, result in the need for sampling of process gas streams at very high pressures, often up to and exceeding 150-400 psia (1.0-2.8 MPa), and at very high temperatures, often up to and exceeding 600-1600xc2x0 F. (320-870xc2x0 C.). The gas streams to be sampled may further contain one or more highly corrosive and/or abrasive constituents.
Previously-known sampling devices and methods are typically inadequate for sampling particulate-laden gas streams at such extreme conditions. For example, known cascade impactors for sampling particulate, such as those shown and described in U.S. Pat. Nos. 3,001,914; 3,693,457; and 3,795,135, which are hereby incorporated by reference herein, often suffer from galling, fusion of contacting components, deterioration of materials, and other damage at extreme conditions. For example, previously known samplers typically include separate spacer elements between adjacent stages, and/or separate spacer elements between the jet plate and associated collection substrate of a single stage. These spacer elements are commonly in the form of cross-shaped supports or rings that are placed between adjacent components of an impactor during assembly. These spacer elements may undergo fusion or material transfer by galling with adjacent components at elevated temperatures, potentially resulting in analysis errors. In addition, the numerous components of a typical impactor render assembly and disassembly time consuming and subject to error or damage.
In addition, previously-known cyclone samplers at best provide limited utility in high-temperature, high-pressure sampling applications. For example, a prior art five-stage cyclone assembly included threaded connections on each of its five cyclone separators, which require disassembly by unthreading these connections to access and analyze the particulate matter collected therein. Threaded connections typically present on such samplers have been found to seize due to galling from exposure to high-temperature gas streams. In addition, the cyclone separators of the conventional five-stage cyclone assembly are laid out on the manifold in a longitudinally-spaced arrangement that results in an overall sampler length that has been found unacceptable for in-situ sampling in certain process vessels. Still further, the configuration and materials of construction of the conventional five-stage cyclone assembly provide inadequate structural rigidity, and the assembly may deform under its own weight at high temperatures.
Through considerable experimentation, applicants have discovered advantages in combining two or more devices into a single sampling system, thereby overcoming constraints imposed by in-situ, isokinetic sampling at high-temperature and high-pressure. For example, a cyclone sampler or a cascade impactor can be operated in series with an alkali vapor collector, as described in greater detail elsewhere herein, with the outlet of the cyclone sampler or cascade impactor communicating with the inlet of the alkali collector. Previously-known sampling devices are generally unsuited for use in combination in this manner. For example, the combination of an alkali collector with the conventional five-stage cyclone assembly would require substantial modification, and would result in an unacceptable sampler length.
Thus it can be seen that needs exist for improved sampling devices, methods and systems. It is to the provision of improved sampling devices, methods and systems that the present invention is primarily directed.
The present invention provides a system, method, and various associated devices for collecting and sampling particulate matter and other characteristics of a fluid. The various aspects of the present invention can be implemented, via remote and/or local control, by a sampling system that may be permanently installed to fluid-handling equipment, or by a portable sampling system designed for temporary and removable attachment to fluid-handling equipment.
By way of example, and without limitation to other applications, the present invention enables isokinetic in-situ sampling of particulate matter from high-temperature, high-pressure process gas streams generated in power-generation facilities. The present invention allows determination of fluid characteristics, such as particulate loadings, particle size distributions, and alkali vapor content. Separate samples may be taken upstream and downstream of a PCD, sequentially or simultaneously, to evaluate the particulate-removal performance of the PCD. Sampling can be conducted for a number of reasons, such as regulatory compliance, to prevent equipment damage, or to monitor for performance degradation or failure of a PCD.
The present invention provides a compact sampler suited for use in confined spaces, and can be configured for remote and/or local control and monitoring. Optionally, the sampling system of the present invention can be configured as a portable system adaptable for use with a variety of fluid handling vessels. Alternatively, the system can be permanently installed. Multiple devices can be combined in a single sampling system according to preferred forms of the present invention. For example, an alkali collector can be coupled with a particulate sampling device, with the inlet of the alkali collector receiving fluid discharged from the particulate sampling device. The particulate sampling device can take the form of a cyclone separator, a cascade impactor, or a total-mass sampler according to various forms of the present invention. For example, a cyclone sampler may be advantageously employed upstream of a PCD for collection and analysis of the relatively higher particulate loading in the fluid stream prior to treatment by the PCD, and a cascade impactor or a total-mass sampler employed downstream of the PCD where particulate loadings are relatively lower, thereby obtaining the benefit of the collection capacity of the cyclone sampler and the sensitivity of the cascade impactor and the total-mass sampler.
Briefly described, one aspect of the present invention provides a cyclone sampler for sampling particulate matter from a fluid. The cyclone sampler preferably includes a manifold having at least one conduit for communicating a stream of fluid containing particulate matter. The sampler preferably also includes at least one cyclone subassembly for collecting a sample of particulate matter. Sacrificial connection means are preferably provided for releasably connecting the cyclone subassembly to the manifold. The provision of the sacrificial connection means and the elimination of threaded connections provides improved high-temperature performance, reducing or eliminating heat-induced damage and/or fusion of components.
The cyclone subassembly preferably includes a housing having a first end comprising an entry port and a second end comprising an access opening. The cyclone subassembly preferably also includes a generally conical cyclone chamber within the housing, having an inlet and an outlet, and bounded by a sloping sidewall. The cyclone subassembly preferably also includes a collection cup communicating with the outlet of the cyclone chamber and with the access opening of said housing. Preferably also included is a cap for closing the access opening, and sacrificial connection means for retaining the cap within the access opening.
In still another aspect, the present invention provides a cascade impactor for analyzing particulate matter in a gas stream. The cascade impactor preferably includes a housing having an inlet for receiving a gas flow, a flowpath communicating the gas flow through the housing, and an outlet for discharging the gas flow. The cascade impactor preferably also includes at least one jet plate within the flow path. The cascade impactor preferably also includes at least one collection substrate, each collection substrate being within the flow path downstream of an associated jet plate, each collection substrate having at least one slot therethrough and at least one impact surface. Each jet plate and each collection substrate preferably also include alignment tabs, which cooperate with alignment means for aligning the alignment tab of each said jet plate with the alignment tab of the associated collection substrate. The alignment tabs make assembly and disassembly of the impactor easier and faster, and reduce the possibility of incorrect assembly.
Each jet plate for the cascade impactor preferably includes a body portion having a first surface, a second surface, and at least one opening extending therethrough. The jet plate preferably also includes an integral spacer depending from the first surface. The integral spacer can take the form of, for example, a circumferential lip, and/or first and second diametrical ribs. The provision of the integral spacers facilitates assembly and disassembly, and reduces the possibility of incorrect assembly. The susceptibility to heat-induced damage and resultant errors in analysis are typically also reduced by the provision of the integral spacers. Each collection substrate for the cascade impactor preferably has at least one passage therethrough, at least one impact surface, and an alignment tab.
In yet another aspect, the present invention provides a total-mass sampler for analyzing particulate matter in a gas stream. The total-mass sampler preferably includes a housing having an inlet for receiving a gas flow, a flowpath communicating the gas flow through the housing, and an outlet for discharging the gas flow. The total-mass sampler preferably also includes a particle collection filter within the flow path. The total-mass sampler preferably also includes a perforated metal plate downstream of the particle collection filter to support the filter. The exemplified total-mass sampler does not split the sample into different particle-size fractions and is capable to collecting samples that are larger than the samples collected in either the exemplified cyclone sampler or the exemplified cascade impactor.
In another aspect, the present invention provides an alkali vapor collector for analyzing an alkali vapor content of a gas stream. The alkali vapor collector preferably includes a housing for attachment to an external support, the housing having an inlet for receiving a sample of a fluid. The alkali vapor collector preferably also includes a quantity of activated bauxite or activated alumina disposed within the housing and exposed to the sample of fluid, and a fluid-impervious liner between the housing and the bauxite or alumina. The provision of the liner advantageously reduces damage to the housing that might otherwise result from contact with alkali-bearing vapors and/or condensate. The provision of the liner also advantageously minimizes loss of alkali vapor on the inner metal surfaces of the housing, which could lead to erroneous measurements of the alkali vapor content of the gas.
These and other features and advantages of preferred forms of the present invention are described herein with reference to the drawing figures.